Process of metal coating glass



April 20, 1937. P. DEREN PROCESS OF METAL comma GLASS.

Filed Oct. 21, 1935 2 Sheets-Sheet 1 April 0, 1937- P. DEREN PROCESS OFMETAL COATING GLASS Filed Oct. 21, 1935 2 Sheets-Sheet 2 Patented Apr.20, 1937 UNITED STATES PATENT OFFICE I raocass or 56m Guess PincusDeren; Magnolia, Mass., assignor, by

mesne assignments, to Birdseye, Electric Corporation, Dover, M, acorporation of Delaware Application October 21, 1935, Serial No. 45,947

9Claims.

I This invention consists in a novel process of applying a metallicreflecting coating to selected areas of glass articles. One importantfield of use for the invention is in connection with the 6 insidesilvering of electriclamp bulbs, and for purposes of illustration itwillbe described as it is carried out in this field.

It has been the practice heretofore in silvering lamp bulbs to apply ametallic coating to substan- 10 tially the entire inner surface of thebulb and s then in a subsequent operation to define the selectedreflecting areas by removing portions of the coating by mechanicalmeans,as by a rotary scraping tool. Such a scraping operation, besidesrequiring considerable mechanical skill on the part of the operator andbesides being relatively slow, is practically limited to bulbs ofconcen; trio and symmetrical shape, although a considerable proportionof the bulbs containing an internal reflector integral with the bulb aredesigned for particular purposes and have particular shapes that are notsurfaces of revolution about the main axis of the bulb. Moreover, indealing with the symmetrical bulbs there is always present a danger ofscratching and even breaking thebulb by the scraping tool employed.

Accordingly an object of the present invention is to make available achemical process for quickly and effectively removing the-coating fromcertain exposed areas of the bulb surface while protecting the coatingin the selected areas where it is to be retained. In one aspecttherefore, the

process of my invention consists in the steps of depositing a metalliccoating on a larger area of the article than that eventually required,protecting. the included selectedvarea by covering it with a non-aciddiluting or neutralizing medium and then treating the exposed surfacewith an acid which is diluted and rendered inactive at the boundaries ofthe selected area.

In carrying out the process .of my invention I prefer to utilize an acidwhich is in itself a strong acid and a strong oxidizing agent. Nitricacid happens to be both, and iswholly suited for the requirements of thecase. For protecting the selected areas -of the coating I may use anyalkaline solution having the capacity to neutrallze nitric acid at therate it is supplied for dissolving the metallic coating. For thispurpose atcaustic solutionfsuch-as sodium hydrate entirely satisfactory.

The nitric acid may be applied to the exposed silver surface in avariety of ways. Preferably it should be strong and used in the smallestquantities that will accomplish the result. In

no case should any large quantity be flowed or sprayed into the bulb,since there would be a tendency for rivulets to form and run down thesides of the bulb and into thev neutralizing solution with suflicientvelocity to exist momentarily as nitric acid, below-the line ofprotecting solution, and an irregular line with discolored edges mightresult. The acid may be used'in small quantities-not more than 2 tocubic centimeters for say a 500 watt lamp bulb,-as a liquid, and shouldnot be sprayed with any more force than isnecessary to cause it tospread over the entire exposed surface. The action of strong nitric acidis very rapid on such a thin coating, and much less than the abovesuggested amount is sufllcient to change the deposit to water solublesilver nitrate.

If desired, the nitric acid may be applied in vapor form or as mixedvapor of nitric acid and water, by leading the vapors from a boilingflask of the nitric acid into the space in the bulb above the.protecting solution. This may be most easily accomplished byhaving asmall vapor tube pass up through the neck and main part of the bulbholding the protecting solution, and enclosed within a larger tubecontaining air only. This serves to insulate the small tube containingthe hot vapors'from' the main body The vapor method is in some wayssuperior, in

that very small quantities can be used and it "is certain that all partsof the exposed silver will be reached and dissolved by this very smallamount of acid. f Moreover, the rate of attack of the silver is morerapid, as well as more certain, because of the higher temperatureemployed. The safety is greater, and the amount of total acid and alsoof protecting causticemployed will be less, thus reducing costs.

The nature and scope of my invention will be best understood andappreciated from the following description of the manner in which it maybe carried out in providing a lamp bulb with a reflecting surfacedisposed in a peripheral zone extending substantially from its line ofmaximum diameter to a line in the neck of the bulb.

In the accompanyingdrawinga- Fig. 1 is a view of aninvertedbulb invertical cross section. in position on the apparatus. Fig. 2 is a viewin side elevation, partly in section, of the completed bulb, and v Fig.3 is a view similar to Fig. 1 showin a modified form of apparatus.

The bulb Iii is shown in Fig. 1 as being provided with a coating l I ofmetallic silver extending substantially over its entire inner surface.The bulb 'shown in Fig. 1, also acts as a stopper and comprises'a rubberwasher l2 interposed between a main portion l3 and a downwardly movablehead ll. when the head I 4 is drawn downwardly the washer l2 is expandedinto firm engagement with the walls of the neck of the bulb, thus makinga liquid-tight seal. A vertical tube l5 extends upwardly through thestopper from a two-way cock i6, which, in turn, is connected with asupply pipe I! and an overflow pipe l8. When the cock is turned intofull-line position as shown in Fig. 1, the protecting solution, which inthis case may be sodium hydrate, is admitted to the interior of the bulbuntil the latter is filled approximately to its line of maximumdiameter, or to any other selected level.

A tube l9 also passes vertically through the stopper and into the upperpart of the bulb to a point somewhat above the end of the tube ii. Thetube I9 is preferably provided with a spray nozzle and may be arrangedto act as a vent during the introduction of the caustic solution to thebulb, and then to supply an acid spray to the exposed walls of the bulbabove the level of the caustic solution. when the bulb'has been filledto the desired level with the caustic solution, the two-way cock isturned to the dotted line position shown in Fig. 1 in which the overflowpipe [8 is connected to the tube I! so that the tube l5 itself now actsas an overflow pipe determining the liquid level of the caustic solutionand as a vent for the bulb. Nitric acid is now introduced under pressurethrough the tube IS in such a manner as to thoroughly wash the exposedportion of the bulb, dissolving the metallic silver therefrom andleaving the glass entirely free of metallic silver upon its innersurface above the liquid level of the caustic solution. As the acidflows down the walls of the bulb it is diluted and neutralized by thecaustic solution at the surface level of the latter, while the metalliccoating below the line of the surface level is thus protected from theacid and maintained intact.

The operation of removing the surplus silver from the exposed surface ofthe bulb may be performed quickly and completely and the reflectingcoating thus limited to a zone defined by the protecting causticsolution. The silver-containing 50 acid escapes from the bulb throughthe overflow pipe l8, where it will be collected for reclaiming or reuseas desired. At the conclusion of the operation, the caustic solution,which has now served its intended purpose, may be drained from 55 thebulb and the latter removed from its stopper.

The completed bulb is shown in Fig. 2 with the silvered zone ll definedon its upper edge in this case at a line coinciding substantially withthe line of maximum bulb diameter. The lower edge 60 of the silveredsurface, in the neck of the bulb,

may be conveniently determined in the, step of,

applying the silvered coating, or it may be formed by scraping thesurplus silver from the neck or in any other convenient manner v t5 InFig. 3 is shown a somewhat modified form of apparatus designedparticularly for removing the metallic coating from the desired areas ofthe bulb by hot nitric acid vapor. It will be under- I stood that inpractice the apparatus is set upin 70 multiple form and that perhaps onehundred bulbs are simultaneously treated. One unit only of the apparatusis herein illustrated.

The bulb ill, with its inner surface coating ll of metalliesilver, isshowndn Fig. 3 as mounted in is inverted position upon a stopper 2!, Twotubes enter the bulb through its stopper, the tube 22 beingsubstantially flush at its inner end with the end of the stopper andserving as a supply and discharge pipe for the caustic solution. The

larger tube 23 is an overflow pipe and determines the level to which thecaustic solution may be admitted and it also acts as a casing for asmaller concentrically arranged tube 24 having a perforated nozzle 25which extends above the end of the tube 23 into the open space in thebowl of the bulb. Through this tube 24 hot nitric acid vapor is admittedto the interior of the bulb and this acts at once to dissolve allmetallic silver which is exposed above the liquid level of the causticsolution. A

The tube '22 is provided with a two-way cock 26 leading to a dischargepipe 21 and a caustic which is inserted a discharge pipe 33 and throughwhich also passes the acid supply tube 24. Both the discharge pipes 33and 21 may be arranged to discharge through a single funnel 34 to areclaiming tank, not shown.

In using the apparatusof Fig. 3 the following steps are preferablycarried out. Valve 3| .is closed and, with the cook 26 in the positionshown, the valve 29 is opened to admit caustic solution 20 to the levelof the overflow tube 23. The large tube 23 acts as an overflow formaintaining a constant level of the solution held in the bulb. When thebulb is filled to the proper level, small amounts of nitric acid vaporare admitted through the inner small tube 24, from a source not shown.The silver coating the bulb on the surface above the line of the causticis rapidly attacked and changed to water soluble silver nitrate. Thecaustic protects the rest of'the silver coating on the bulb at asubstantially even line around the bulb. I

Before drawing off the caustic solution, through tube 21, the nitricacid still adhering to the surface of the bulb above the desired line,must be has been withdrawn, .and so injure or remove some of the silvercoating of the protected area.

This can be easily accomplished by gehtly open ing the valve whichconnects to a source of air under pressure oi a few pounds per squareinch above atmospheric. A few bubbles of air passed through the body ofthe protecting caustic solution are efiectiveto splash the caustic overthe surface of the top of the bulb, wash down into the caustic solution"the dissolved silver and neutralize any excess nitric acid.

The caustic solution may now be withdrawn from the bulb by turning thecock 26 so that it passes through pipe 21 to the collecting funnel 34and to a suitable receiver. The caustic so removed can be used over anumber of times, preferably by maintaining its caustic strength byadditions of fresh caustic. Moreover, most ofthe dissolved silver willbe found at the bottom of this reservoir of used caustic in the form ofprecipi- "tated silver hydrated oxides, from which it may flow downthe'tube and through pipe 21 and can be collected in the storage tankfor used caustic and silver residues.

Water for washing is now allowed to flow with considerable force throughthe small tube 2d and tip.25 from a source and connection not shown.This wash water leaves the bulb through the pipe 38, but it must bediverted from flowing to the container for used caustic and silverresidues, by changing suitable connectionsnot shown-since otherwise thecaustic would be too much diluted for further use, and silver recoverywould be made 10 more difiicu'lt. When all chemicals havebeen removed,the bulb is rinsed with distilled water.

throughtube 24 and tip 25, by making other changes in the externalconnections-not shownand following the rinsing air, which can be heatedif desired, is forced through the same tube 24, by

any suitable arrangement of connections, until the interior of the bulbis entirely dry. The air will leave the bulb by the same pipe 33 andwill be dissipated into the atmosphere at the open connection at thefunnel 34.

If it is desired to produce a bulb having a pcripheral silvered surfaceextending over its curved end, as is often required for indirectlighting, the process of my invention may be carried out with the bulbin, upright position by filling the bowl thereof with caustic solutionand then spraying nitric acid into the neck of the bulb in sucha manneras to cause it to flow over thewalls of the bulb andremove the silvertherefrom down to the line of maximum diameter or other predeterminedlevel. The silver-containing acid is neutralized at the caustic leveland pumped from the bulb as fast as it accumulates.

The bulb during this silver-removing operaample, for the purpose ofremoving silver from a predetermined area defined by the line assumed Iof a surface of revolution around the axis of the bulb, could be readilytreated as disclosed above, although it would be almost an impossibilityto 50 remove the silver from such a bulb by mechanical means. The samecan be said of a bulb havin v a frosted or any other irregular androughened surface on the inside, over which the silver has beendeposited.

I do not specifically illustrate further applications of my novelprocess, but contemplate its use suitably modified in the production ofselected areas of any desired shape or location upon glass articles, andparticularly upon electric lamp bulbs.

60 While I have specifically referred only to silver as a metalliccoating to be treated, the process of my invention is not limited-inthat respect but may be usefully employed in" connection with rhodium orother reflecting metals or alloys by suitable modification oftheprotecting solution, on the one hand, and the acid or dissolvingsolution on the other hand.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is,-

1. The process of coating with metal selected areas of lamp bulbs, whichconsists in depositing a metallic coating upon the inside of the bulb,filling the bulb to a predetermined level with an tion could be in ahorizontal position, for ex Moreover it is apparent that a" alkalinesolution, and treating the remainder of the bulb with an acid to removethe coating fr'om the exposed portions of the bulb.

2. The process oi inside silvering the bowl end surface of a lamp bulb,which consists in silver coating the interior of the bulb, filling thebulb to a predetermined level with sodium hydrate, and

then washing the remainder of the bulb with face of the lamp above theoverflow level with an acidsolution,

4. The process of metallic coating selected areas of the innersuriace oflamp bulbs of unsymmetrical shape, whichis characterized by the steps ofdepositing metal upon a liarger area of the bulb surface than iseventually required, flooding with a caustic solution the selectedareas, and flowing acid upon the remainder of the bulb surface, thusdissolving surplus-metal from the bulb except where it is protected bythe caustic solution while the latter neutralizes the acid at theboundaries of the selected areas.

'5. The process of metallic coating selected areas of a lamp bulb, whichconsists in depositing metal upon a larger area than that eventuallyrequired, immersing the included selected area in a protective causticsolution, treating the exposed metallic areas with an acid to dissolvethe metal, and then, before drawing'the caustic solution, neutralizingacid remaining upon the treated areas. s

6. The process of defining selected silvered areas in an, insidesilvered'bulb, which consists in flooding the selected area with aliquid caustic solution, and exposing sllvered areas in the enclosedspace above the liquidilevel of the caustic solution to nitric acidvapor which is thus neutralized at the boundaries of the selected areaby the caustic so1ution,,..

7-. The process of making lamp bulbs with metal reflecting areas ofpredetermined shape, which consists in applying. a metallic coating toan area large enough to include the desired selected area, filling thebulb with a caustic solution up to a level defining the selected area,and then introducing nitric acid vapor into the space abovethe causticsolution.

tallic reflecting areas, which consists in silvering the bowl of thebulb, then filling the bulb to a predetermined llquid level with acaustic solution,

eventually required in the reflector, immersing the selected reflectingarea in a liquid alkaline solution up to a predetermined liquid levelline, and then washing the unimmersed walls of the-bulb with an acidsolution effective to remove the deposited metal therefrom down to thelevel of the a PINCUS pm. I

alkaline solution.

55 8. The process of making lamp bulbs with mep

